This invention relates generally to a sealing assembly, and more particularly, to a sealing assembly for use with a pressurized vessel.
One known pressurized vessel is a syngas cooler. In at least some known syngas coolers, a regulated nitrogen purge, with a controlled flow rate, is directed into an annular space defined between a shell and a tubecage of the cooler from the top of a cooler vessel. The nitrogen purge maintains a substantially continuous and circumferentially uniform positive flow through the annular space to prevent syngas from flowing into the space and creating pockets of corrosive gases. If an effective area of the annular space is too large to achieve the uniform, positive flow with a limited flow rate of nitrogen, a seal may be used to minimize the size of the entrance into the annulus from the bottom of the cooler. Furthermore, stresses induced in the tubecage and/or in the shell by the seal must be below the yield strength of the tubecage and/or shell. Moreover, after lightoff of a gasifier, there may be a transient event during which a syngas pressure wave travels through the cooler and creates a large pressure difference across the tubecage. During this event, a seal may be used to relieve the pressure differential across the tubecage by accommodating syngas backflow into the annular space.
At least two known seals designs are used in syngas coolers to restrict the syngas flow from the bottom of the cooler into the annulus. The first of such seal designs uses a pinched ring of fiber insulation material that extends from the tubecage and makes contact with a plate extending from a cooler vessel wall. The plate slides vertically to enable the seal to accommodate thermal expansion of the tubecage. The seal also includes at least one relief valve that enables syngas to flow into the annular space during a syngas backflow at lightoff. However, in such a seal, the moving parts that control the relief valve(s) may become corroded and/or clogged with particulate matter.
The second of such known seal designs includes a hinged ring of folded metal plates, called “pillows,” that are coupled to an inner support ring on the tubecage and that contact the cooler vessel wall. During syngas backflow, the pillows pivot upwards on the hinges, and away from the vessel wall, to relieve the pressure on the tubecage. After the backflow, the pillows pivot downward and re-establish contact with the vessel wall. However, such a seal design is prone to failure, as the pillow may become stuck in the open position. As such, positive uniform flow of nitrogen purge gas is not maintained, and thus allows a constant flow of syngas into the annular space, which may cause dew point corrosion of the vessel wall. Furthermore, in such a seal design, the effective area for flow between the pillows and the vessel wall may be of a size that the nitrogen purge may not have a uniform positive flow through the seal.
As such, neither of the known seal designs is typically able to achieve a successful nitrogen purge of the annular space. Furthermore, the effectiveness of both of the known seal designs may be limited as a result of particle buildup and/or plugging.